Field of the Disclosure
The present invention relates generally to semiconductor devices. More specifically, examples of the present invention are related to image sensors with enhanced quantum efficiency.
Background
Image sensors have become ubiquitous. They are widely used in digital still cameras, cellular phones, security cameras, as well as, medical, automobile, and other applications. The technology used to manufacture image sensors, has continued to advance at great pace. For example, the demands of higher resolution and lower power consumption have encouraged the further miniaturization and integration of these devices.
One type of image sensor, the complementary metal oxide semiconductor (CMOS) image sensor, is very popular in commercial electronics. However, as these semiconductor devices have scaled downward, photodiode area has also decreased resulting in a lower incident photon count on each photodiode. Several challenges for down-scaled CMOS image sensors are maintaining low-light sensitivity and reducing image noise—two problems exacerbated by a low incident photon count.
The use of conventional light filter arrays (e.g. red, green, and blue arrays) arranged in known patterns (such as a Bayer pattern or the like) may result in decreased light absorption by the image sensor. This is the product of each light filter only permitting the passage of a small range of visible wavelengths. For instance, a red light filter may permit passage of 750 nm-650 nm photons, but block out the remainder of the visible spectrum. Similarly, a green filter may permit the passage of 500 nm-600 nm photons, but block out the remainder of the visible spectrum. As such, the use of conventional light filter arrays may provide for relatively inefficient absorption of visible photons incident on the image sensor. Similarly, a green filter may permit the passage of 500 nm-600 nm photons, but block out the remainder of the visible spectrum. As such, the use of conventional light filter arrays may provide for relatively inefficient absorption of visible photons incident on the image sensor.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention.